600XL 64 KB memory upgrade

[TrailMyx]

Since I've been collecting retro computers for a long time now and I've developed my "favorites" over that time.  I'm not a great expert at the Atari 8-bit line, but the 600XL has turned into my favorite 80's computer to collect.  The main reason I like it as much as I do is because of the small size compared to the other Atari 8-bit computers up to this point.

However, there are a couple limitations that make the 600XL not as desirable as you might have with an original 800 or the 800XL.  Mainly the limited memory of only 16Kbytes.  Thankfully this limitation is fairly easy to fix given how the original 600XL hardware was designed.  Just 3 lifted pins, 1 lifted resistor and 3 jumpers is all you need as well as acquiring (2) 64Kx4bit DRAM chips to replace the existing 16Kx4bit DRAMs found on a stock 600XL.  The second limitation is the only video out is through the RF connection which I've found on nearly 1/2 of my 600XLs to be VERY poor quality.  My next guide will be to explain the best way I've found to add both SVIDEO and composite video to make this particular computer the most ideal version of an Atari 8-bit.

I originally found this information on Youtube by Flashjazzcat where he chronicles the modification.  I wanted to add a bit more details to the "why" this mod exists other than just the jumpers/changes.  For some really good videos describing all sorts of Atari 8-bit mods, be sure to follow him at Youtube

This simple mod can be broken down into 4 separate steps:

• Lift pin 3 of U5 (74LS158) and jumper to A14 of ANTIC (U9 pin 19) - note the vias used for A14 and A15 in the attached photo
• Lift pin 10 of U6 (74LS158) and jumper to A15 of ANTIC  (U9 pin 20)
• Lift pin 8 of U16 (74LS51) and jumper to lifted leg of R36 (see #4)
• Lift bottom leg of R36 (closest to DRAM chip U11

Here is the schematic changes from the above modification:



Finally you should have procured (2) 41464 64Kx4bit DRAM chips.  I have used THESE chips from Jameco.com successfully.  These are direct replacements for the 4416 DRAM chips found in U11 and U12.

Once complete, your mod should look something like this: